<VV> Valve Noise

[pete]

I have a 1968 500, 110 HP. My current problem is that when the engine gets very hot (i.e. after several miles highway driving) there is considerable valve rattle when accelerating. This does not occur when the engine is cold or on short local runs. I have recently replaced the valve pushrod 'o' rings and set the pushrod gaps cold according to the procedure given in the Corvair Basics book. Again, there is no valve noise whatsoever when the engine is cold. I have re-checked the point gap and also the crankshaft pulley and everything seems fine. Any ideas what is going on here? The engine supposedly has about 69,000 mi.

Pete